Older circuit breakers with conventional solenoid operated trip coils frequently placed a typically red light in series with the trip coil. A trickle of current is allowed to flow through the solenoid coils and illuminate the light as a basic diagnostic indicator of the tripping circuit. Should the trip coil fail, the red light would extinguish and operators making routine checks would detect the failure and take corrective action. Such a system detects one particular type of failure, an open circuit in the system. Such an open circuit would by its nature disable the tripping function.
New circuit breakers with self-diagnostics are not limited to this type of failure, but may have a breaker trouble or a binary (on or off) “ready” or “not ready” contact to signal an abnormal condition requiring corrective action. Unfortunately, particularly on retrofit circuit breaker applications, there was no way to incorporate this “not ready” contact into the existing control scheme or of inserting it into the tripping circuit to turn off the red light without also losing the ability to trip the breaker, even in the case of abnormal conditions which ordinarily would not otherwise prevent tripping the circuit breaker. Occasionally, a user has opted to preserve the apparent functionality of the red light by putting the “ready” contact in series with the red light (and thus with the trip input) to extinguish this light for the purpose of signaling a warning or failure from the circuit breaker diagnostic system. This has the unfortunate consequence of also disabling the ability to trip the breaker electrically, even if the cause of the “not ready” condition may not be one which prevents the breaker from tripping. Prior retrofit applications in which circuit breakers with self-diagnostics have been used to replace a conventional circuit breaker which had a red light in series with the trip coil have generally ignored the advantages of self-diagnostics because of the above limitation.
Thus, there is a need to provide in a circuit breaker with self-diagnostics, a method to signal an abnormal condition using the existing red light circuit while retaining the ability to trip the circuit breaker either manually or in the event of an overcurrent condition when the cause of the unusual condition signaled is not one which prevents tripping the circuit breaker.